ARGX-121

ARGX-121 is a first-in-class monoclonal antibody developed by argenx that targets immunoglobulin A (IgA). Its mechanism of action involves binding to IgA and promoting its degradation via the neonatal Fc receptor (FcRn) pathway. This process leads to enhanced endocytosis and lysosomal degradation of IgA, resulting in rapid and significant depletion of circulating IgA levels—over 90% reduction within one week has been observed in preclinical models. The drug leverages the efgartigimod backbone technology, aiming for broad therapeutic potential in diseases where pathogenic IgA plays a role. As of early 2025, ARGX-121 is in preclinical development with Phase 1 studies expected to begin in the second half of 2025[2][4][5].